1. Field of the Invention
The present invention relates to supporting devices of rotors and more particularly, to a supporting device used for supporting a rotor of an apparatus such as a heat-dissipation fan.
2. Description of Prior Art
FIG. 1 is a schematic exploded diagram of a conventional heat-dissipation fan, wherein a rotation shaft 101 of a fan body 100 is supported by a pair of axial bearings 103 fitted into two ends of a sleeve 102, and is rotated by a ring magnet (not shown) fitted on the inner surface of the fan body 100 repelled by a magnetic force generated by a coil 104 coupled to the fan body 100.
In order to cooperate with the axial begs 103, the rotation shaft 101 is usually made of a sintered metal, and requires delicate processing. However, the fan body 100 is usually formed by usually made of plastics and is generated in manufacturing small fans often due to the very thin wall of the fan body 100.
In addition, lubrication between the rotation shaft 101 and the axial bearings 103 is reduced by the effect of consumed lubricants due to easily heat production during the fan rotating at high speed for long time, which also causes damage and deformation by the heat to the rotation shaft 101 and the axial bearings 105 later on, and which generates shaking and noise, and shortens the usage life of the fan. Therefore, defects of being labile to high temperature, being labile to abrasion, easily generating shaking and noise, and having a short usage life may be concluded.
In order to improve the above defects of a conventional heat-dissipation fan, “Improved stature of fan motor” as stated in Chinese Patent Publication No. 285375 discloses a rotational device comprising a ceramic axial sleeve and a ceramic axis inserted in said sleeve, with defined sure roughness for the axial sleeve and the axis. Addition of lubricants is still required for the axial sleeve and the axis of the “Improved structure of fan motor” to reduce frictional noise and heat production. Also, said patent defines only the surface roughness of the axial sleeve and the axis, but not the corresponding spacing between the axial sleeve and the axis. According to experiments proceeded by the inventor of the invention it has been found that even if completely following the defined surface roughness for making the axial sleeve and the axis shaking and noise will still be generated if the corresponding spacing between the axial sleeve and the axis is too big. In addition, the solid ceramic axis of said patent is brittle and is not easily fixed on the fan body in manufacturing small fans due to the very thin wall of the fan body